Method for heat treating bearings and product thereof



United States Patent METHOD FOR HEAT TREATING BEARINGS AND PRQDUCTTHEREOF Lucien Pei-as, Billaucourt, France, assignor to Regie Nationaledcs Usines Renault, Billancourt, France, French works No Drawing.Application July 25, 1956 Serial No. 599,912

Claims priority, application France September 7, 1955 3 Claims. (Cl.148-2155) Rings for bearing balls and rollers are at present almostgenerally made of steel having the following composition: carbon 1%Crabout 1.30%Mn about 0.40%-silicon content less than 0.40%.

Before being ground to the final dimensions, the balls and rollers aresubjected to a hardening treatment, followed by tempering at a lowtemperature around 150 C. and their hardness, measured on the Rockwellmachine by the penetration of adiamond cone under a load of 150 kg. liesbetween 62 and 67.

Bearings made in this way are very satisfactory to ensure the goodrunning of mechanisms which only have to withstand a moderatetemperature. But as soon as the temperature of a bearing in operationexceeds 180 C., the bearing surfaces wear very rapidly and the bearingsthemselves become unfit for use in a very short time; very often, infact, the mechanism in which they are used deteriorates through thefriction and the shocks which, themselves, result from the eccentricitycreated by increases in play caused by wear.

According to the invention, rings and rollers are so constituted that,without abnormal wear, they can withstand continuous service attemperatures decidedly higher than those which formerly it was notpermissible to exceed; to this end the steel, according to theinvention,

0, percent Si, Mn, Cr, Mo,

percent percent percent percent and may have, as a non-limiting example,the following composition:

Percent Si 1.4 Mn '04 which is very suitable.

The elaboration, rolling, drawing, tempering, and

machining of steels of this kind can be carried out'without anydifliculty by present techniques.

After being machined approximately to the final dimensions, the piecesare subjected to heat treatment by 2,844,500 Patented July 22, 1958being brought to a temperature between 820 and 900- C., followed byquenching, and possibly tempering at between 180 and 250 C. The desiredvery fine distribution of carbides, not dissolved during the quenchingtreatment is obtained if the rings, balls, or rollers, have beenpreviously normalised by heating to a sufliciently high temperature, atleast 900 C., in order to dissolve the carbides, and then cooling inair.

In a general manner, the temperature chosen for heating before quenchingis 50 to 80 higher than that of the completion of eutectoidtransformation on heating.

Quenching is generally carried out in oil, but in the case of balls itis more advantageous if water is used for this purpose. The quenching ofthe rings can be done by steps, a salt bath at a temperature of 180 C.being the first cooling medium, the ambient air the second.

A very great hardness is obtained when quenching, by whatever means itwas carried out, is followed by cooling to a temperature below -20 C.

After treatment, the machining is completed on the grinding wheel andwith the usual polishing methods until the desired final dimensions areprecisely obtained.

Bearings manufactured according to the invention, from steels with ahigh carbon content and a silicon content which is comprised between0.80 and 2.0%, withstand, without any abnormal wear, temperatures whichmay rise to 250 C., while the usual bearings of carbon chromium steelcannot withstand, without damage, temperatures above 180 C. With thecase-hardened steels which are sometimes used for bearings, the workingtemperature can scarcely rise above 150 C.

The table below shows hardnesses, after the quality heat treatment andafter one hundred hours heating at 4 250 C. carried out as a test afterthe heat treatment, of steels, some of which contain the smallquantities of silicon which are usual, and some of which have a siliconcontent in conformity with the invention.

7 Composition RC hard- Hardness ness after after heating treatment forhours 0 Si Mn Cr M0 at 250 after heat treatment 0.96 0. 34 0. 44 1.150.05 66 57. 8 1.00 0. 28 0. 35 traces 1. 70 65. 5 59. 7 1.06 1. 42 0.48traces traces 65. 5 62 1.00 1. 36 0. 41 traces 1. 71 66 62. 4 0. 96 0.87 0. 30 traces 1. 05 66 62 It is worthy of note that a composition,such as that shown in the third line, can be used, since thiscomposition does not include any noble alloying constituent element, itis of particular interest on account of its low cost.

The advantage of the steels of the invention appears clearly when it isknown that the 62 Rockwell hardness is that which extensive experiencehas shown to be necessary for good practical behaviour of bearings.

The bearings according to the invention can be used with great advantageparticularly in the construction of gas turbines.

I claim:

1. A process of treating bearings consisting essentially of 0.8 to 1.3percent carbon, 0.8 to 2.0 percent silicon, 0.2 to 0.8 percentmanganese, 0 to 3 percent chromium,

0 to 2.5 percent molybdenum and the remainder substantially iron whichcomprises heating said hearings to a temperature of from 50 to 80 C.above the eutectoid transformation temperature, quenching said bearingsat a temperature from 180 to 250 C. and cooling said bearings at atemperature below 20 C.

2. A process of treating bearings consisting essentially of 0.8 to 1.3percent carbon, 0.8 to 2.0 percent silicon, 0.2 to 0.8 percentmanganese, 0 to 3 percent chromium, 0 to 2.5 percent molybdenum and theremainder substantially iron which comprises heating said bearings to atemperature of from 820 to 900 C'., quenching said bearings at atemperature of from 180 to 250 C. and

cooling said bearings to a temperature below 20 C. 3. A heat treatedbearing element produced by the process of claim 1.

References Cited in the file of this patent UNITED STATES PATENTSEdmunds Feb. 2, 1937 Bonte Mar. 23, 1948 Svenson Jan. 6, 1953 FOREIGNPATENTS Great Britain Nov. 30, 1928

1. A PROCESS OF TREATING BEARINGS CONSISTING ESSENTIALLY OF 0.8 TO 1.3PERCENT CARBON, 0.8 TO 2.0 PERCENT SILICON, 0.2 TO 0.8 PERCENTMANGANESE, 0 TO 3 PERCENT CHROMIUM, 0 TO 2.5 PERCENT MOLYBDENUM AND THEREMAINDER SUBSTANTIALLY IRON WHICH COMPRISES HEATING SAID BEARINGS TO ATEMPERATURE OF FROM 50 TO 80*C. ABOVE THE EUTECTOID TRANSFORMEDTEMPERATURE, QUENCHING SAID BEARINGS AT A TEMPERATURE FROM 180 TO 250*C.AND COOLING SAID BEARINGS AT A TEMPERATURE BELOW -20*C.